Textbook Question
How many stereoisomers are possible for c. a ketotriose?
28. Carbohydrates
Monosaccharide
4:19 minutesProblem 48d,e
Textbook Question
Use Figure 23-3 (the D family of aldoses) to name the following aldoses.
(d) the enantiomer of D-galactose
(e) the C5 epimer of D-glucose
Verified step by step guidance1
Identify the structure of D-galactose from Figure 23-3. D-galactose is an aldohexose with the specific configuration of hydroxyl groups on its chiral centers.
To find the enantiomer of D-galactose, invert the configuration at every chiral center. This means if a hydroxyl group is on the right in D-galactose, it should be on the left in its enantiomer, and vice versa.
Name the enantiomer of D-galactose. Since enantiomers are mirror images, the enantiomer of D-galactose is L-galactose.
Identify the structure of D-glucose from Figure 23-3. D-glucose is also an aldohexose with its own specific configuration of hydroxyl groups.
To find the C5 epimer of D-glucose, change the configuration of the hydroxyl group at the C5 position only, while keeping the rest of the molecule the same. The C5 epimer of D-glucose is D-mannose.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldoses
Aldoses are a type of monosaccharide characterized by the presence of an aldehyde group (-CHO) at one end of the molecule. They can exist in various forms, including D and L configurations, which refer to the orientation of the hydroxyl group on the chiral carbon farthest from the aldehyde. Understanding aldoses is crucial for identifying their structural relationships and naming conventions.
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Enantiomers
Enantiomers are a pair of molecules that are non-superimposable mirror images of each other. In the context of sugars, D-galactose and its enantiomer, L-galactose, differ in the configuration around all chiral centers. Recognizing enantiomers is essential for naming aldoses correctly, as it affects their biochemical properties and interactions.
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Epimers
Epimers are a specific type of diastereomer that differ in configuration at only one of several chiral centers. For example, D-glucose and D-mannose are C2 epimers, while D-glucose and D-galactose are C4 epimers. Identifying epimers is important for understanding the structural diversity of sugars and their relationships, particularly when naming aldoses based on their stereochemistry.
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